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Estimation of the upper ocean heat budget from one year of observations at a moored
array in the north central Arabian Sea shows a rough balance between the horizontal
advection and time change in heat when the one-dimensional balance between the surface
heat flux and oceanic heat content breaks down. The two major episodes of horizontal
advection, during the early northeast (NE) and late southwest (SW) monsoon seasons,
are both associated with the propagation of mesoscale eddies. During the NE monsoon,
the heat fluxes within the mixed layer are not significantly different from zero, and the
large heat flux comes from advected changes in the thermocline depth. During the SW
monsoon a coastal filament exports recently upwelled water from the Omani coast to the
site of the array, 600 km offshore. Altimetry shows mildly elevated levels of surface eddy
kinetic energy along the Arabian coast during the SW monsoon, suggesting that such offshore
transport may be an important component of the Arabian Sea heat budget.
The sea surface temperature (SST) and mixed layer depth are observed to respond to
high frequency (HF, diurnal to atmospheric synoptic time scales) variability in the surface
heat flux and wind stress. The rectified effect of this HF forcing is investigated in a
three-dimensional reduced gravity thermodynamic model of the Arabian Sea and Indian
Ocean. Both the HF heat and wind forcing act locally to increase vertical mixing in the
model, reducing the SST. Interactions between the local response to the surface forcing,
Ekman divergences, and remotely propagated signals in the model can reverse this, generating
greater SSTs under HF forcing, particularly at low latitudes. The annual mean
SST, however, is lowered under HF forcing, changing the balance between the net surface
heat flux (which is dependent on the SST) and the meridional heat flux in the model.
A suite of experiments with one-dimensional upper ocean models with different representations
of vertical mixing processes suggests that the rectified effect of the diurnal
heating cycle is dependent on the model, and overstated in the formulation used in the
three-dimensional model.

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Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2000

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